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Microacoustic devices have widely been investigated as a means of sensing mechanical, chemical, and electrical liquid properties. Shear-horizontally polarized modes might be used to avoid radiation losses into the liquid. If an acoustic waveguide is applied on top of the propagation surface, those modes can be converted into Love waves. Love mode devices can be designed to show one of the highest sensitivities among all microacoustic sensors while providing high mechanical robustness and being chemically inert. Good candidates for piezoelectric substrates are several Y-rotated quartz cuts as well as 36°YX-LiTaO3. SiO2 is a superior guiding layer because of low damping and excellent chemical and mechanical resistance. Besides high sensitivity, low temperature dependence is crucial in order to overcome the need of precision temperature control. This leads to the scope of the present work: Based on both experimental and theoretical results, the specific properties of various temperature-compensated YZ'-quartz/SiO2 and 36°YX-LiTaO3/SiO2 systems are discussed. For quartz based devices, temperature compensated systems could be realized with any sensitivity up to 80 % of the specific maximum, whereas the coupling coefficient being the limiting factor. In opposite, 36°YX-LiTaO3/SiO2 systems yield high coupling for any system of interest to sensor applications. However, there is only one temperature compensated configuration. This particular system provides a sensitivity of about 50% of the maximum of quartz based devices. In summary, for both material systems device configurations could be identified which combine high temperature stability, a suitable coupling coefficient, and high sensitivity.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
